A moving contact line (MCL) is a moving line of intersection between a fluid/fluid interface and a solid wall. MCLs are central to a wide range of flows in nature and industry, ranging from surface coating, spray cooling, displacement of oil by CO2, to the recent development of 3D printing, microreactors, and nanotechnology. However, the modelling of MCLs has been a classical challenge. In particular, when the solid phase can dissolve into the wetting fluids, e.g. in soldering, formation of alloys and manufacturing of composite materials, there are still a few fundamental challenges which have handicapped the development of predictive computational models. This project will address those challenges and it has three objectives:
(1) to develop a new comprehensive computational model for 3D direct numerical simulations (DNSs) of MCLs on dissolvable solid surfaces, covering both inertial- and diffusion-dominant dissolutive wetting regimes and resolving nanometer length scales associated with MCLs.
(2) to develop a novel experimental method using high-speed imaging to directly measure the interface profiles during the dynamic dissolutive wetting line, and then formulate a rigorous theory to relate the dynamic contact angle and interface profiles to system parameters.
(3) to formulate a reduced-order macroscale computational model which can save computational effort by at least nine orders of magnitude compared with DNS models in numerical simulation of dissolutive wetting
All three research objectives have been addressed. A comprehensive computational model for 3D simulations of the droplet shape for dissolutive wetting is developed. Our numerical results shows good consistence with the experimental results. Then, a macroscopic model to predict the time evolution of the droplet shape for dissolutive wetting is formulated, avoiding the direct numerical simulation from the micro scale to macro scale, and its efficiency can be increased by 6 orders in two dimensions and 9 orders in three dimensions. The effects of macro-scale parameters (surface tension, diffusion coefficient and viscosity, etc) on the droplet height under the dissolutive wetting condition are also studied, leading to deep understanding on the dynamics of the dissolutive wetting.
